java—在尝试自动连线时获取spring托管类上的nullpointer

e4yzc0pl  于 2021-07-23  发布在  Java
关注(0)|答案(3)|浏览(443)

我正在创建一个spring-boot应用程序来侦听rabbit队列并将消息转发到kafka流。我正在努力 @Autowire Kafka配置类，但我得到 NullPointerException ，更令人惊讶的是，当我列出所有spring管理的bean时，它会给出我正在尝试的类的对象名 @Autowire . 我不知道我在哪里失踪了。
起始类：

  1. @SpringBootApplication
  2. @ComponentScan(basePackages = {"com.example.demo.service","com.example.demo.configuration"})
  3. public class RabbitConsumerApplication {
  5.     private static ApplicationContext applicationContext;
  7.     public static void main(String[] args) {
  8.         applicationContext = SpringApplication.run(RabbitConsumerApplication.class, args);
  9.         displayAllBeans();
  10.     }
  12.     public static void displayAllBeans() {
  13.         String[] allBeanNames = applicationContext.getBeanDefinitionNames();
  14.         for(String beanName : allBeanNames) {
  15.             System.out.println(beanName);
  16.         }
  17.     }
  19. }

kafkaproducerservice类：

  1. package com.example.demo.service;
  3. @Component
  4. public class KafkaProducerService {
  6.     @Autowired
  7.     private KafkaTemplate<?, String> kafkaTemplate;
  9.     public void getMessageFromMQ(Message  message) throws InterruptedException {
  11.         Map<String, Object> configProps = new HashMap<>();
  12.           configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
  13.           configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
  14.           configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
  15.           DefaultKafkaProducerFactory<Object, Object> defaultKafkaProducerFactory = new DefaultKafkaProducerFactory<>(configProps);
  17.         kafkaTemplate.send("testTopic",new String(message.getBody()));
  19.     }
  21.     @Override
  22.     public String toString() {
  23.         return "KafkaProducerService [kafkaTemplate=" + kafkaTemplate + "]";
  24.     }
  26. }

kafkaproducerconfig类：

  1. package com.example.demo.configuration;
  3. @Configuration
  4. public class KafkaProducerConfig {
  6.     @Bean
  7.     public ProducerFactory<String, String> producerFactory() {
  8.       Map<String, Object> configProps = new HashMap<>();
  9.       configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
  10.       configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
  11.       configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
  12.       return new DefaultKafkaProducerFactory<>(configProps);
  13.     }
  15.     @Bean
  16.     public KafkaTemplate<String, String> kafkaTemplate() {
  17.       return new KafkaTemplate<>(producerFactory());
  18.     }
  19. }

rabbitlistenerservice类：

  1. package com.example.demo.service;
  3. public class RabbitListenerService implements MessageListener{
  5.     @Autowired
  6.     private KafkaProducerService kafkaProducerService;
  8.     @Override
  9.     public void onMessage(Message message) {
  10.         System.out.println("message :"+new String(message.getBody()));
  11.         System.out.println("object:"+kafkaProducerService.toString());  //19th line. getting nullpointer on this line   
  12.     }
  14. }

堆栈跟踪：

  1. 2021-02-20 13:55:06.750  WARN 5392 --- [tnerContainer-1] s.a.r.l.ConditionalRejectingErrorHandler : Execution of Rabbit message listener failed.
  3. org.springframework.amqp.rabbit.support.ListenerExecutionFailedException: Listener threw exception
  4.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.wrapToListenerExecutionFailedExceptionIfNeeded(AbstractMessageListenerContainer.java:1746) ~[spring-rabbit-2.3.4.jar:2.3.4]
  5.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:1692) ~[spring-rabbit-2.3.4.jar:2.3.4]
  6.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.actualInvokeListener(AbstractMessageListenerContainer.java:1562) ~[spring-rabbit-2.3.4.jar:2.3.4]
  7.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.invokeListener(AbstractMessageListenerContainer.java:1539) ~[spring-rabbit-2.3.4.jar:2.3.4]
  8.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doExecuteListener(AbstractMessageListenerContainer.java:1530) ~[spring-rabbit-2.3.4.jar:2.3.4]
  9.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.executeListener(AbstractMessageListenerContainer.java:1474) ~[spring-rabbit-2.3.4.jar:2.3.4]
  10.     at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.doReceiveAndExecute(SimpleMessageListenerContainer.java:967) ~[spring-rabbit-2.3.4.jar:2.3.4]
  11.     at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.receiveAndExecute(SimpleMessageListenerContainer.java:913) ~[spring-rabbit-2.3.4.jar:2.3.4]
  12.     at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$1600(SimpleMessageListenerContainer.java:83) ~[spring-rabbit-2.3.4.jar:2.3.4]
  13.     at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.mainLoop(SimpleMessageListenerContainer.java:1288) ~[spring-rabbit-2.3.4.jar:2.3.4]
  14.     at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.run(SimpleMessageListenerContainer.java:1194) ~[spring-rabbit-2.3.4.jar:2.3.4]
  15.     at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
  16. Caused by: java.lang.NullPointerException: null
  17.     at com.example.demo.service.RabbitListenerService.onMessage(RabbitListenerService.java:19) ~[classes/:na]
  18.     at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:1688) ~[spring-rabbit-2.3.4.jar:2.3.4]
  19.     ... 10 common frames omitted
  21. message :hey you
  22. message :hey you

我只是想 @Autowire kafkaproducerservice类进入rabbitlistenerservice。

Javaspringspring-bootAutowired

3条答案

按热度按时间
sqserrrh

sqserrrh1#

好吧，我解决了这个问题。即使@autowire发生了，但它实际上绑定了一个空对象，因为在rabbitconfig.java中，我实际上用一个新关键字初始化了rabbitlistenerservice，而spring ioc不处理它。我改变了方式，解决了问题。
rabbitlistenerservice.java文件

  1. @Component
  2. public class RabbitListenerService implements MessageListener{
  4.     @Autowired
  5.     private KafkaProducerService kafkaProducerService;
  7.     @Override
  8.     public void onMessage(Message message) {
  9.         System.out.println("message :"+new String(message.getBody()));
  10.         System.out.println("object:"+kafkaProducerService.toString());
  12.         try {
  13.             kafkaProducerService.getMessageFromMQ(message);
  14.         } catch (InterruptedException e) {
  15.             // TODO Auto-generated catch block
  16.             e.printStackTrace();
  17.         }
  18.     }

然后将rabbitlistenerservice自动连接到rabbitconfig
rabbitconfig.java文件

  1. @Configuration
  2. public class RabbitConfig {
  4.     private static final String my_queue = "TestQueue";
  6.     @Autowired
  7.     private RabbitListenerService rabbitListenerService;
  9.     @Bean
  10.     MessageListenerContainer messageListnerContainer() {
  12.         SimpleMessageListenerContainer simpleMessageListenerContainer = new SimpleMessageListenerContainer();
  13.         simpleMessageListenerContainer.setConnectionFactory(connectionFactory());
  14.         simpleMessageListenerContainer.setQueues(myQueue());
  15.         simpleMessageListenerContainer.setMessageListener(rabbitListenerService);
  16.         return simpleMessageListenerContainer;
  18.     }
  20. }
展开查看全部
赞(0）分享  回复(0）举报  2021-07-23
f8rj6qna

f8rj6qna2#

从您的代码来看，您似乎还没有定义任何kafka模板bean。例如：

  1. @Configuration
  2. public class MyKafkaConfig {
  4.     ...
  6.     @Bean
  7.     public KafkaTemplate<String, String> kafkaTemplate() {
  8.         // define a template here
  9.     }
  10. }

定义的kafka服务具有注入（自动连线） KafkaTemplate<?, String> . 这样的bean是在配置类中定义的吗？
也请张贴您的stacktrace。

赞(0）分享  回复(0）举报  2021-07-23
6gpjuf90

6gpjuf903#

试试这个，把包换成 * ，确保它在bean列表中打印kafkaproducerservice，
经常练习为impl服务类创建接口

  1. @Component
  2. public class KafkaProducerServiceImpl implements KafkaProducerService

例如

  1. @SpringBootApplication
  2.     @ComponentScan(basePackages = "com.example.demo.*"})
  3.     public class RabbitConsumerApplication {
  5.   ...
  6.     }
赞(0）分享  回复(0）举报  2021-07-23
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